Preventing distorted signals and wandering zero in cable telegraphy



Feb. 18, 1930. H@ ANGEL 1,747,853 PREVENTING Ds'lokfwEDf SIGNALS AND'wANbx-:RING ZERO 1N CABLE TELEGRAPHY .File June 3. 1927 2 sheets-sheet 1 P12/Rody Recez V017 akku/nag Feb. 1s, 1930. H. ANGEL 1,747,853

PHEVENTING'DITORTED SIGNALS vA ND WANDERING ZERO IN CABLE TELEGRAPHY Filed June 3, 1927 2 sheetsfsheet 2 60 w. Peralta/e1' T 'I www 7" 'M-wi? geni? ,8* 3fm Patented Feb. V1.8,

UNITED STATES PATENT Y OFFICE i HERBERT ANGEL, BROOKLYN, NEW YORK, ASSIGNOR TO THE WESTERN UNION TELE- GRAPH COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK P'REVENTING- DISTORTED SIGNALS AND WANDER-ING ZERO IN CABLE TELEGRAPHY Application filed June 3,

The invention relates to signalling systems and more particularly to the transmission of telegraph impulses over long cables.

lt is well known that at high speed of transmission over a long cable, the signalling cable is unable to discharge itself as rapidly as the signals are being transmitted. As a result, a charge gradually collects on the cable which results in a shitting of the Zero position from the true Zero to a value, either above or below,idepending upon the character and speed of impulses. This phenomena is known as the wandering zero.7 Considerablel distortion ot the signal wave shape is .produced at the receiving apparatus due to this wandering zero, and, if left to continue, the signal becomes kso distorted at the receiving apparatus that inaccurate signal recording results.

The diiiculties experiencedwith the wandering Zero are partially overcome by employing as signalling codes, impulses of reversepolarity. This type of Vcode considerably aids the cable in discharging impulses.

Such a signal code would be ideal it each impulse'were of the reverse polarity trom thev preceding one and of the same length. The result would be periodic, positive and negative'impulses which would enable-the cable to discharge and by the very character of the impulse, would prevent a wandering of the Zero line.

However, the Morse code comprisesy dash impulses represented in this code by impulses of the same polarity following each other. In such cases ay greater charge of one polarity is impressed upon the line than ot the opposite polarity, with the result that the cable tends to gather a charge either of one polar- 40 ity orthe other depending upon the impulses. An `arrangement tor minimizing the effect of the wandering Zero is provided by employing condensers connected inthe line at both ends ofthe cable. These condensersif properly designed with respect to the capacityot the cable itself, will so react with the cable as to prevent the accumulation of av charge in the cable and thereby prevent the wandering zero eiect. Y vNot only; is the speed ot signalling consid- 1927. Serial No. 196,224.

erably impeded, by reason of the wandering zero eiect noted above, but, due to other inherent characteristics of the cable such as inductive surges from adjoining regions, the wave shape ot the signal is considerably distorted, so much so that attimes it is impossible to detect ythe true wave shape at the receiving end.

In order to overcome this diiiiculty, provision is made in the form of correcting networks comprising condensers and inductances in the cable `circuit at the transmitting end which function to impress a wave shape of such a character on the cable that after being affected by the distorting eifects noted above, it will be received at the receivingend in true wave shape. This is further aided by employing a similar correcting net-work at the receiving end of the cable. rlhe resultant effect of the network for impressing a predetermined wave shape at the transmitting end. and a network at the receiving end for correcting the wave shape, results in a waveV shape approximating that kimpressed on the cable by the transmitter.

Here againhowever, considerable ditiiculty is experienced by reason ot the fact that while the correction ot the wave shape to overcome the distorting effects is made, thel inherent wandering zero etect ot' the receiving instrument plus the wandering Zero produced in the cable by earthcurrents, etc., still distorts the signal impulse.. It is therefore highly desirable to provide some arrangement whereby the wave shape can be corrected for distortion while at the same time the wandering zero effect is eliminated.

An object ot my invention is to provide means for producing a pure wave at the receiving end of the line similar to the wave shape of the transmitted impulse.

Another object of my invention is to provide in a system for transmitting impulses over a long cable at a high speed, means for approximating the wave shape ot the transmitted impulse.k v y YStill another object of my invention is to provide a method of telegraph signalling over a long cable which comprises the step of correcting for the distortion induced in the cable, repeating the corrected wave and thereafter correcting for the wandering zero effect.

Other objects of my invention which to gether with the foregoing will appear in the specilication which follows in which Fig. 1 is a circuit diagram showing circuit arrangements and the apparatus for correcting for distorted wave shapes.

Fig; 2 shows circuit arrangements and apparatus for correcting for the 'wandering zero effect, and

i Fig. 3 shows the circuit arrangement and apparatus for the preferred form of my invention in which the wandering Zero eifect is eliminated while at the same time the wave shape of the impulse is properly7 corrected.

Referring to Fig. 1, a transmitting station A, and a receiving station B are shown connected by a cable 1. At the transmitting station there is provided a battery 2, arranged to impress voltages of predetermined wave shape upon the cable 1 under control of the armatures R and R1 of transmitting relays (not shown). These armatures R and R1 may be operated in any of the well known Wheatstone transmitting arrangements, such for example, as shown in the patent to Benliamin f 1,447,747. Connected between the sending relays` and the cable 1, is a sending condenser 3 which is shunted by the sending condenser shunt resistance 4. By properly designing the sending condenser 3 and resistance 4, the signal impressed on the cable 1 can be made of such a. shape that the vdistorting el'l'ects thereon will produce a corrected wave shape at the receiving end, approxi mating the shape of the wave impressed by the sending relays R and R1. j

At vthe receiving end B of the cable,`there is provided a primary receiving instrument 5 which may be of any suitable type, such for instance as the Heurtley hot wire type, sim ilar to that shown in the patent, No. 1,029,123. This isai'ranged in the well known manner to repeat the impulses received over the line 1 in accordance with the character of the impulses received. Arranged between the cable 1 and the primary receiving instrument 5, is a receiving condenser 8, shunted by a resistance 9. The receivingcondenser 8 and the resistance 9 comprise a correcting network which functions to correct for distortion to the waveshape produced in the transmission of the signals over the cable. Shunted across the primary receiving instrument 5 is a resistance 10 and an inductance shunt 11, which corrects for the distortion of the wave shape in the primary receiver 5.

The conductors 6 and 7, connected to the secondary receiving instrument 12-conduct the'signals repeated under the control of the primary receiving instrument 5 for operating the relay armature 13 to either of its contacts 14 or 15, in accordance with the imarmature 13 moves into engagement with its.

left or right hand contact, for making a record of the received signals. The recording instrument is connected to the midpoint of the battery y17 and in series with either winding 18 or 19 depending upon the contact with whichthe armature 13 engages. The windings 18and19 control the movement of the armature 'contacts 20 and 21 respectively, which in turn, control a local circuit in a well known manner. `Since this is not part of the present invention, the local circuit is not shown in detail. v

It will be noted from the above arrangement that although a correcting network is provided at the transmitting and receiving end for correcting for the wave shape of the received signal, no provision is made for overcoming the effect of the wandering zero, with the result that the impulse repeated over the conductors 6 and 7 by means of the primary receiving instrument ,fis distorted, not only due to the wanderinggzero of the lcable itself, but also to the wandering zero effect of the primary receiving instrument 5. This distorted signal is repeated to the secondary receiving instrument for operating the recording device and local receiving apparatus. d

Fig. 2 shows a circuit arrangement and apparatus vfor overcoming the wandering zero effect. In this figure, the stations A and B are connected by the cable 1, of such length that as the speed of transmission is increased, the capacity of the cable does not permit of sufficiently rapid discharge of the current impulses and produces, as a result, the wanderingA zero effect.

The sending apparatus at station A, as before, comprises two armatures R and R1 controlled by relays which may be operated by a standard Vheatstone transmitter arrangement similar to that described in the patent referred to above, and are arranged to impress impulses of reverse polarity from the battery 2 as well understood. Connected between the transmitter at station A and the cable 1,.is a sending condenser 26, which, as will be noted, is unshunted.

At the receiving end B there is kprovided a primary receiving instrument 5 of any standard type such as the Heurtley type,

ywhich is arranged to repeat the received impulses over the conductors 27 and 28 in acsistance 10 and an inductance shunt l1 are connected in shunt to the primary receiving instrument 5 to correct for distortion of the received impulse wave shape.

The main winding 32 of the secondary receiving instrument is connected-in the circuit of conductors 27 and 28'in series vwith a local condenser 33 shunted by a resistance 34.

The armature 35 of the secondary receiving instrument 30, as it engages one or the other of its contacts 36 and 37, controls a recording instrument 38 and local relays 39 and 40, which in turn control local circuits over the armatures 4l and 42 respectively. Since this portion of the circuit is well known and is not part of my invention, it is not shown in detail.

The secondary receiving instrument 30 comprises in addition to the main winding 32, a secondary winding 43, which `is connected in a local correcting circuit 44. In this modification it will be noted that the sending condenser 26 and receiving condenser 29 are unshunted for the purpose of preventing wandering zero eiiects. In practice however, it has been found that owing to the fact that the condensers are unshunted the cable has no means for shaping the signals during the transmission of the signals through the cable, a condition which results in producing` a surge and wandering zero eiiect at the re` cei'ving end with the result that the impulse received at the primary receiving instrument is distorted considerably in wave shape from that impressed upon the cable at the transmitting end by the transmitting apparatus.

In order to partially correct for such. distortion of the signalling wave, a local correcting `network 44 is provided which is arranged to reshape the distorted signal in the secondary circuit. Due to the local shunted resistance 34 of thel condenser 33, thel inherent wandering zero effect produced in theA pri'- mary receiving instrument 26 itself plus the wandering eectsof the cab'leare impressed across the main winding 32 of the secondary receivinginstrument so that the armature 35 is moved'i'n response toa partially distorted wave.

For the purpose` of overcoming the diii- A transmitted atl high speed. aredistorted in Connected betweenwave' shapeandwhich is subject tothewan'- dering zero eifect. The sending relays at the transmitting station A are illustrated conventionally as in the previous figures. The armatures R 'and R1 control the polarity of the impulse impressed upon the cable from the battery 2 in accordance with the position assumed by these armatures under control of the sending relays in the well known manner. Connected between the cable .andthe sending apparatus is a sending condenser 3 shunted by a resistance element 4. This network O condensers and resistances is of such similar to'that shown in the patent to I'Ieurt-` ley referred to above, and which is arranged to control the circuits 50 and 51 in accordance with the impulses received over the cable for operating the secondary receiving instrument in a manner to be described in detail hereinafter.

Connected between the primary receiving instrument 5 and the cable is receiving condenser 8 shunted by a resistance 9. The receiving network 8, 9, and the primary receiving instrumenty 5 are shunted by a resistance element 10 and an inductance 1l. This network is such as to correct for the distortion of wave shape of impulses transmitted over the cable.

Connected in the circuit 50 and 5l is the main winding 56 of the'secondary receiving instrument 57.- In addition to this main winding, the secondary receiving instrument is also provided with a secondary local winding 58 which is connectedinthe local correcting circuit 59 which is controlled by the armature 60 of the secondary receiving instrument. A local unshunt-edv condenser 61 is also connected inthe circuit ofy the conductors 50 and' 51 in series with the main winding 56 ot the secondary receiving instrument l57.

Thearmature 60 under control of the windings 56 and 58 engages either the contacts 62 or 63 in accordance with the receivedv impulses, thereby perating the recorder 64 in series with either the winding of relay 65 or relay 66, andthe armatures 67 and 68 in turn control the local circuits. Since these local circuits are not a part of my main invention, it is unnecessary to illustrate them indetail.

It will be seen by a comparison ofy the organization shown in Fig. 3 withy those shown in Figs. l and 2, that the' desirable ieatures'` of those circuits' are incorporated inV Fig.` 3 while overcoming the defects of each. The network 3, 4, at-the transmitting end andthe network 81,9?, l0, 141- at the' receiyingendifcorrect for the distortion of the Wave shape of the impulse impressed upon the cable so that the impulses for operating the receiving ins rument are of a Wave shape closely resembling the impulses impressed upon the. cable at the transmitting end. However, since a complete circuit is provided, the condensers being shunted by resistances, no correction is here made for the Wandering zero eiiect of the cable as Well as that of the receiving instrument. By inserting the unshunted condenser 6l in the local circuits 5() and 5l of the output of the primary receiving instrument 5, Vthe Wandering Zero eiiiects oi' the primary receiving instrument and of the cabler are prevented from entering the main Winding 50 of the secondary receiving instrument 5.7.

The secondary receiving instrument in this case is actuated through its amain Winding 56 by condenser impulses through the local unshunted condenser 6l. To reconstruct these impulses into their original shape the local correction circuit 59'is employed simulating as nearly as possible the shape of the signal impressed at the transmitting end of the line, and the armature 60 is therefore operated accurately in accordance with the impulses sent into the cable at the transmitting station A.

It will be obvious to engineers that instead of eliminating the Wandering zero effect by means of the unshunted condenser 61 I may connect the leads 50, 5l to the Winding 56 through a suitable transformer, the condenser and the transformer being diiierent forms of transient energy transfer devices.

Although the invention has been shown in connection With a telegraph system, it is obvious that it has more general application, as in any signalling system wherein a long cable is employed over Which impulses are to be transmitted ata very high rate of speed, such that the impulses are distorted due to the capacity eli'ect of the cable and other eX- traneous influences and in which it is desired to correct for the distorted wave shapes.

I claim l. In a signalling system, a first station, a remote station, a signalling line having a Wandering zero characteristic, a signal receiving apparatus at a second station responsive to impulses transmitted over said cable from said irst station, an output` circuit connected to said receiving apparatus into which said impulses are repeated, a secondary receiving instrument in said output circuit and means including an unshunted condenser connected in said output circuit of said receiving apparatus operating to time the impulses Supplied to said secondary instrument and for nullifying the ei'ect for said Wandering zero.V

2. In a signalling system, a cable over which signals are distorted due to Wandering zero, a receiving apparatus arranged to be operated by said impulses, an output circuit or repeating the impulses received by said receiving apparatus, a secondary receiving instrument in said output circuit, and an unshunted condenser connected in said output circuit operating to produce a definite timing of the impulses supplied to said secondary instrument and for preventing the passage of said Wandering zero.

8. In a signalling system, a cable over hich signals are distorted due to Wandering Z o, a signal receiving apparatus arranged to be operated by said impulses, an output circuit for repeating the impulses received by said receiving apparatus, a secondary electromagnetic instrument in said output circuit and unshunted condenser means connected in said output circuit for nullifying the eiect of said Wandering Zero.

t. In a signalling system comprising a signaliing conductor over which impulses are distorted and which is subject to the Wandering zero effect, a signal-actuated receiving apparatus, a correcting network connected between said receiving apparatus and said cabe for `correcting for said distorted Wave shape, means controlled by said signal-receiving apparatus for repeating the impulse received from said receiving instrument and means including an unshunted condenser for correcting said repeated impulse for the Wanderin Zero eliect.

5. In a telegraph system, a. transmitting station, a receiving station, a cable subject to distortion and Wandering Zero connecting said transmitting and said receiving stations, means at said transmitting station for impressing signalling impulses on said cable, a network at said transmitting station for modifying said transmitted impulse to produce a predetermined Wave shape, a primary signal-actuated receiving instrument at said receiving station, a network at said receiving end for correcting for said distorted Wave shape, a repeating circuit controlled by'said primary receiving instrument for repeating said impulses, a secondary signal repeater in said repeating circuit and means including an unshunted condenser in said repeating Vcircuit for correcting for said Wandering zero effect on said received impulse.

G. In a telegraph system, a transmitting station, a receiving station, a cable subjected to distortion of the Wave and Wandering Zero effect, a condenser at the transmitting station, a resistance shunting said condenser', a condenser at the receiving station, a resistance shunting said condenser, an inductance shunt associated therewith, said condensers and shunt at said transmitting and receivingstations land said inductance being arranged to produce a pure or natural shaped signal, a primary signal-actuated receiving Yinstrument arranged to be operated by said lUO signals, a secondary receiving instrument controlled by said primary receiving instrument and a local Condenser connected in the circuit of said secondary receiving instrument to supply impulses of equal duration and for preventing the wandering zero effect of the cable and primary receiving instrument from influencing the secondary receiving instrument and a local correction circuit controlled by the output of the secondary receiving instrument for controlling said secondary receiving instrument.

7. In a telegraph system, a transmitting station, a receiving station, a cable subjected to distortion of the wave and wandering Zero effect, a condenser at the transmitting station, a resistance shunting said condenser, a condenser at the receiving station, a resist- Vance shunting said condenser, an inductance shunt associated therewith, said condensers and shunt at said transmitting and receiving stations and vsaid inductance being arranged to produce a pure or natural shaped signal, a primary signal actuated receiving instrument arranged to be operated by said signals,` a secondary signal actuated receiving instrument controlled by said primary receiving instrument and a local unshunted condenser connected in the circuit of said` secondary receiving instrument to supply impulses of equal duration and for preventing the wandering Zero effect of the cable and primary receiving instrument from influencing the secondary receiving instrument.

8. In a signalling system a cable over which the impulses transmitted are distorted by the wandering zero effect and by earth currents, transmitting apparatus including a condenser shunted by a resistance receiving apparatus including a condenser shunted by a resistance, a primary signal-actuated receiving instrument adapted to respond to received block signals, a shunt about said receivingapparatus including an inductance and a resistance connected in series, a secondary signal-actuated receiving apparatus connected to the output of said primary receiving apparatus including an unshunted transient energy transfer device, a secondary receiving apparatus having a winding receiving impulses from said transfer device, a correcting network, an auxiliary coil on said secondary receiving instrumentV connected in the output of the latter through said correcting network.

In testimony whereof I atlix my signature.`

HERBERT ANGEL. 

